Password protect documents

I have recently come across an error when emailing documents to the client. There are 2 pension reports, one relief at source the other salary sacrifice. The emails are consistently failing. I think this is due to the 2 files both being named 'pension summary'. (Case number is still live and looking for a fix). This has lead to another problem - I cannot download the reports as password protected. This is a major problem due to GDPR.